This application relates to a system for charging rechargeable batteries and to an electrical circuit useful in charging rechargeable batteries.
There are many consumer products sold on the market today which are intended for portable use and hence are intended to be primarily powered by electrochemical cells or batteries. Portable radios, calculators, cassette tape recorders, video cameras are but a few examples of these products. Many of these products, while they are intended primarily for portable use and hence are designed to operate from a low voltage direct current source, such as an electrochemical cell or battery, have a need to operate from a source powered from conventional household alternating current. To satisfy this need, typically the product is sold with a separate AC to DC converter which may be interposed electrically between the source of AC power and the product to convert the alternating current to direct current and to reduce the high voltage to a lower voltage compatible with the design of the product.
Historically, many consumer products have been powered by primary or non-rechargeable cells or batteries. In the rather recent past, however, secondary or rechargeable batteries have proved to be particularly suitable for providing power to consumer products. Rechargeable cells or batteries, however, must be recharged when the electrical energy stored in the cell or battery has been expended. In the rather recent past, however, secondary or rechargeable batteries have proved to be particularly suitable for providing power to consumer products. Rechargeable cells or batteries, however, must be recharged when the electrical energy stored in the cell or battery has been expended. Since consumer products of the type described above do not contain any means for recharging the secondary battery, the user must purchase a charging device to accomplish that purpose. The present invention is directed toward a device which will permit the user of the consumer product to utilize the AC to DC converter, sold with the product, as a means for charging secondary batteries.
It is in the art to provide a visual indication that charge current is properly being delivered to the cells or batteries. One problem particularly addressed by the present invention, is that associated with the low voltage delivered by the AC to DC converter. The consumer product is typically designed to operate at the relatively low voltage available from the cells or batteries providing power during portable use. Accordingly then, the AC to DC converter must provide the same relatively low output voltage provided by the cells or batteries during portable use. In many instances, the low voltage provided by the AC to DC converter is not sufficient to contemporaneously provide an acceptable voltage for charging the batteries and sufficient voltage for providing the aforementioned visual indication. The present invention addresses this problem.
Another problem addressed by the present invention is associated with the fact that it is common to charge a plurality of cells or batteries or sets of cells or batteries contemporaneously in the same charging unit. It is possible that the cells or batteries will not be at the same state of discharge. When the sets are connected in a parallel circuit, but not receiving current from the AC to DC converter, current will none-the-less flow from the cells or batteries at the higher state of discharge to the cells or batteries at the lower state of discharge. This flow of current between the cells or batteries connected in parallel, while not detrimental, may cause the indicator mentioned above to provide a false indication that charge current is being supplied to the cells or batteries from the AC to DC converter. The user then will be mislead into believing that charging current is being delivered to the cells when in fact it is not. The present invention addresses this problem.